I know this is an ancient thread but it helped me solve my clock problem and I wanted to add some context.
The "battery" in the GVP Jaws II is indeed a Dallas Semiconductor "Clock-In-A-Can". There are modern equivalents still around but can sometimes be difficult to find. I got lucky and found one on eBay listed as "NEW DS1994L-F5+ 4kb Time Memory iButton". I may have bought the last one as the auction has now ended.
There is a catch with these iButtons and I see some people have had issues making them work. From the factory their oscillator is disabled. You need to enable the oscillator for the clock to advance. Without enabling the oscillator your Amiga can save the current time but the clock in the iButton will not advance.
All you need to enable the oscillator is an Arduino, a few jumper wires and a single resistor. The Arduino code at the following link will program your iButton with no changes:
https://skyduino.wordpress.com/2012/03/17/arduino-tutoriel-1-wire-ds1994/Don't worry about setting the time. The portion of code that enables the oscillator is the important piece. You can set the correct time when you install the DS1994L-F5+ in your accelerator.
